Bipolar disorder (BD) is a highly recurrent, disabling illness, and emerging data indicate that, for women with BD, the perinatal period is particularly destabilizing. Prospective studies have revealed mood episode morbidity in up to 70% of pregnant women with the disorder, and risk of postpartum mania in as high as 50% of cases. Negative sequelae of BD for expectant and new mothers include severe psychosocial impairment, substantial suicide risk, and rates of postpartum psychosis 100 times greater than in the general public. Moreover, infants of pregnant women with BD are significantly more likely to experience adverse outcomes such as preterm birth, small for gestational age, and microcephaly. Despite these risks, as well as expert recommendations for prophylactic mood stabilization at a minimum effective dose throughout the perinatal period, rates of medication discontinuation are as high as 70% among pregnant and postpartum women with BD. Thus, a critical need exists to find ways to increase appropriate treatment engagement among perinatal women with BD. As a first step toward developing interventions that attempt to increase treatment engagement, it is important to understand factors that limit effective treatment utilization. The proposed study would be the first to examine these questions, integrating quantitative and qualitative methods to elucidate the processes by which perinatal women choose to continue or discontinue BD pharmacotherapy. Eighty pregnant women with BD, half of whom recently discontinued their BD pharmacotherapy, will complete assessments during pregnancy and again at three months postpartum that assess medication utilization, BD symptoms, treatment attitudes, and illness-related cognitions. A subset of the overall sample (n=24) will take part in a qualitative interview to obtain more in-depth information regarding women's treatment decisions regarding perinatal BD care. Women's medication providers (n=up to 80) will also be assessed. The three primary aims of this study are: (1) To test the hypothesis that women's illness-related cognitions account for unique variance in medication continuation decisions, over and above clinical characteristics and treatment attitudes; (2) To utilize qualitative measures to further explore the decision-making process and develop a model reflecting the relative contribution of factors influencing medication continuation decisions; (3) To integrate findings from both quantitative and qualitative phases of the research to develop specific recommendations regarding optimal decision support strategies for women and providers. On an exploratory level (4), this study aims to examine associations between prenatal pharmacotherapy continuation and subsequent treatment decisions and maternal symptom, functioning, and birth outcomes at three months postpartum. Ultimately, this project will lead to a more comprehensive understanding of why perinatal women with BD often discontinue pharmacotherapy, as well as specific recommendations for future interventions, such as prenatal decision support strategies, to address this serious problem.